The present invention relates to an intake system for supplying an internal combustion engine with fuel and air and, more particularly, to an intake system of the type having a fuel injector.
Injection type fuel supplying systems for internal combustion engines, offer various advantages such as cleaning of exhaust emissions, saving of fuel, as well as improvements in the engine output and in the driveability, and so forth. For this reason, this type of system is becoming popular as the fuel supplying system for motor vehicle internal combustion engines. Broadly, the fuel injection type fuel supplying systems can be sorted into two types; namely, a multi-point injection type system in which fuel is injected through fuel injectors which are annexed to respective cylinders of an engine, and a single-point injection type system in which the fuel is injected through a single fuel injector which is disposed upstream of an intake manifold.
In order to fully enjoy the above-mentioned advantages of the fuel injection type fuel supplying system, it is essential that the rate of supply of the fuel is accurately controlled. However, it is quite difficult to control the rate of fuel supply at a sufficiently high accuracy for the reasons described hereinbelow.
For instance, when the temperature in the engine compartment of a motor vehicle is raised, the fuel in the fuel passage is heated to generate vapor. Consequently, the fuel injector injects not only the liquid phase of the fuel but also the vapor phase of the fuel stagnant in the fuel passage in the vicinity of the fuel injector. This means that the net amount of fuel supplied into the induction passage is decreased causing a corresponding reduction in the engine output and impairment of the driveability. Furthermore, when the fuel vapor pressure is excessively high or when the volume of the fuel vapor is excessively large, the driver often finds it difficult to re-start the engine after a stop thereof.
To avoid this problem, in, for example, Japanese Patent Laid-Open Publication No. 79666/1983, an intake system is proposed which injects fuel in a vertical direction however, this proposed intake system encounters the following problems.
In the manufacture of motor vehicles and more particularly, passenger vehicles, it is a current trend to decrease the height of the hood or bonnet mainly for aesthetics and aerodynamics. The reduced height of the hood or bonnet, in turn, requires a reduction in the vertical dimension between the air cleaner and the outlets of the intake manifold, i.e., the intake ports opening to the cylinder. The system proposed in Japanese Patent Laid-Open Publication No. 79666/1983 is of the single-point injection type, wherein the induction passage between the outlet of the air cleaner and the common upstream end portion of the intake manifold is bent substantially at a right angle. Namely, the induction passage has a vertical section extending substantially vertically from the air cleaner and a horizontal section extending horizontally to the intake manifold. The vertical section of the induction passage includes a throttle valve chamber in which are disposed a fuel injector and a throttle valve. It is, therefore, understood that the reduction in the vertical dimensional difference between the air cleaner and the intake manifold is attained by reducing the length of the vertical section of the induction passage. The reduction in the length of the vertical section of the induction passage, however, causes the injected fuel to impinge upon the wall in the bend of the induction passage so that a part of the fuel is supplied to the combustion chambers in the form of liquid film. This is quite unfavorable from the view point of emission control.